Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
  • B22D1/00—Treatment of fused masses in the ladle or the supply runners before casting
  • B22D1/007—Treatment of the fused masses in the supply runners
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
  • C21C1/00—Refining of pig-iron; Cast iron
  • C21C1/08—Manufacture of cast-iron
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
  • C21C1/00—Refining of pig-iron; Cast iron
  • C21C1/10—Making spheroidal graphite cast-iron
  • C21C1/105—Nodularising additive agents
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D5/00—Heat treatments of cast-iron
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D5/00—Heat treatments of cast-iron
  • C21D5/04—Heat treatments of cast-iron of white cast-iron
  • C21D5/06—Malleabilising
  • C21D5/14—Graphitising
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C33/00—Making ferrous alloys
  • C22C33/08—Making cast-iron alloys
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C37/00—Cast-iron alloys

Definitions

• the present invention relates to a new method of inoculating an iron foundry (gray or nodular) and especially a cast iron bath contained in a casting device (trough, oven or spoon) arranged between the outlet of an oven Fusion and mold line.
• the inoculation allows modifying the base metallographic structure, and can affect both the shape, size and distribution of graphite in the metal matrix.
• the present invention also relates to a device for practicing said inoculation process.
• inoculants that are incorporated into the cast iron bath during the melting and / or casting process to obtain the desired metallographic structure and ensure the internal health of the pieces.
• Inoculation is defined as the contribution to a metallic bath in the moment prior to the casting of certain alloys to produce changes in the distribution of graphite, improvements in mechanical characteristics and the reduction of the tendency to bleach.
• inoculation The purpose of inoculation is the generation of germination nuclei on which solid phases grow during solidification.
• these germs result from the addition of fine particles of the same phase to solidify. These particles do not dissolve completely, leading to crystal growth.
• the addition of graffiti carbon to an iron smelter at the time of casting promotes the nucleation of graphite in the metal bath and prevents subcooling during solidification.
• the carbon used as an additive must have a high degree of crystallization to generate nucleation germs that allow carbon precipitation in graffiti form
• the inoculation can be carried out inside or outside the mold.
• the traditional method of external inoculation and the most common, is to add inoculant to the metal jet from the transfer or treatment spoon during filling of the pouring spoon. It is about obtaining a homogeneous mixture and a good dilution of the inoculant. This procedure has important limitations that affect both the weight of metal to be treated (not valid for small quantities) and the useful casting time (the fading of the inoculant effect is very rapid).
• the alloying elements increase or decrease the temperature of this saturation point.
• the solubility should be carefully observed.
• the added graffiti carbon dissolves, it loses its properties as a germinant, which implies a rapid decay of its effect in an uncontrolled way depending on the temperature, chemical composition and degree of agitation of the broth. This makes graphite inoculation a little used method.
• This inoculation may be indispensable in extreme conditions of the foundry, such as burnt smelters, with a low content of 0 2 , which cause a weak reaction to germination with oxides.
• the Graphite incorporation should be done just before filling the mold, which implies a low temperature and a short wait for solidification.
• Figure 1 Scheme of a casting distributor with a channel or runner configuration of a casting oven in which a-1 or a-2 indicates that the anode may be upstream or downstream of the cathode; c is the cathode; S is the closing cylinder of the metal outlet bushing to the mold (in English stopper); f is the iron foundry and M the mold.
• Figure 2 Scheme of a casting distributor with a trough configuration in which a-1 or a-2 indicates that the anode can be upstream or downstream of the cathode.
• Figure 3 Scheme of a casting distributor with a tilting casting spoon configuration in which c-1 and c-2 indicate two possible positions of the cathode in the spoon board or in the spoon bowl and a-1 and a-2 indicate the possible positions of the anode.
• Figure 4 Scheme of a laundry distributor with a spoon configuration with transfer to laundry tray in which a and c represent the possible position of the anode and cathode in the laundry distributor and c the position of the cathode in the laundry tray.
• Figure 5 shows a static cooling curve, indicating the evolution of TeLow and Recalescence in a cast iron alloy using the method of inoculation of the invention.
• Figure 6 shows a dynamic cooling curve, indicating the evolution of TeLow and Recalescence in a cast iron alloy using the method of inoculation of the invention.
• the present invention relates in a first aspect to a method for the inoculation of an additive to a cast iron alloy comprising establishing a plasma arc between the surface of said alloy and a cathode of a transferred arc plasma torch disposed in a casting distributor located before the mold line.
• a casting distributor is understood as a casting device disposed between the outlet of a melting furnace and the mold line. It is also understood that the cast iron alloy contained in the casting distributor is moving in the direction of the mold line.
• Said plasma torch comprises an anode partially submerged in the cast iron alloy and a cathode disposed on the alloy.
• the cathode comprises graphite and the anode is any conventional anode.
• the anode comprises graphite and the cathode is any conventional cathode.
• cathode and anode comprise graphite.
• the graphite of the cathode, of the anode or of both contributes to the iron alloy the nucleating additive.
• said additive are carbon species detached from the anode, or cathode or both, and carbon species are understood as those comprising one or more carbon atoms charged with one or more positive charges.
• said graphite is crystalline synthetic graphite.
• the carbon species detach from the cathode, they are incorporated into the alloy by dragging the plasma gas generated by the plasma arc, the cathode part in contact with the crystalline synthetic graphite plasma gas.
• the cathode of the plasma torch is arranged on the metal surface at a variable height at will, from which an electric arc is generated that impacts the surface of the cast iron alloy.
• This cathode has a central hole along its entire length through which a plasmid gas is introduced, preferably an inert gas (nitrogen, argon ..).
• a plasmid gas preferably an inert gas (nitrogen, argon ..).
• the regulation of the contribution of carbon species from the cathode is carried out by controlling the power of the applied plasma torch and the flow rate of plasmid gas used at each moment, both acting directly proportionally as the contribution increases in the as the cathode temperature and the gas carrying capacity respectively. In this way identical results can be obtained by balancing the gas flow and the applied power. If working with low power it is necessary to increase the gas flow to accelerate the drag effect; on the contrary, with high powers, the flow rate must be reduced to maintain the same volume of carbon species contribution.
• the nucleating additive is released from it and incorporated into the iron alloy by contact of the anode with the cast iron alloy, the part of the anode in contact with the graphite cast iron alloy comprising, preferably crystalline synthetic graphite. .
• the anode is the second electrode of the plasma torch and its principle of contribution of carbon species differs from the principle of the cathode by its function and arrangement in the whole. Since the current circuit closes through the anode that is submerged in the cast iron alloy, this implies two important differences from the cathode. In the first place there is no arc at the tip of the anode, and therefore the temperature in the contact area of the anode with the cast iron alloy is significantly lower than that of the cathode, since it is permanently cooled with the alloy of cast iron that surrounds it.
• the anode is solid and this implies that the dragging function of the plasmid gas that occurs in its case in the cathode as described above, is replaced by the abrasion and dilution exerted by the cast iron alloy in its movement. at the laundry distributor.
• the inoculation power of the anode is fundamentally based on the ability of the system to incorporate into the cast iron alloy the fair and necessary amount of inoculant required at each time of casting.
• the anode can be immersed in the alloy at will, without changing the power setpoint or other electrical variables. The result is that the anode area (graphite area) exposed to the abrasive action of the cast iron alloy can be controlled in a discretionary and immediate manner.
• the nucleating additive is released from both the anode and the cathode through the mechanisms mentioned above for the individual embodiments of graphite anode and graphite cathode, thus adding the inoculant effects of both electrodes. (anode and cathode).
• the anode and the cathode can be arranged such that the radiation of the plasma arc generated in the cathode acts on the non-submerged part of the anode causing heating of the anode (for example, the anode and cathode being housed in the same chamber ).
• the volume of incorporation of graphite species is further favored by the high temperature that is reached in the non-submerged part of the anode and which is transmitted by conduction to the submerged part in the alloy. This temperature is directly proportional to the power applied in the plasma arc since said heating is mainly caused by radiation from the arc. Therefore, in those provisions in which anode and cathode are located in the same chamber, the control of the degree of inoculation must contemplate this variable due to its high incidence in the acceleration of the process.
• the variables involved in the mechanics of inoculation are the flow rate, speed and temperature of the cast iron alloy, on the one hand, and the applied power, the flow rate of plasmid gas, the distance between anode and cathode and the contact surface of the anode with the cast iron alloy on the other.
• the control of the operation is carried out by adapting the working parameters of the plasma system to the needs imposed by metallurgy and the flow of cast metal in real time, maintaining at all times the precise degree of inoculation in the metal arranged for immediate casting. This inoculation procedure allows to reach levels of precision and reliability far superior to the existing standards in the market
• the process of the invention can in principle be carried out in any conventional laundry distributor.
• the casting distributor has a configuration selected from: 1) channel or runner of a casting oven; 2) a casting trough (for example Tundish); 3) a tipping laundry spoon; Y
• an important advantage of the process of the invention is that it allows the unit and variable management of the electrodes (anode and cathode), and of the indicated conditions and parameters: plasma torch power, pouring flow, casting temperature and submerged anode surface area, which results in absolute control of inoculation.
• the procedure allows to have a wide range of possibilities of contribution of Carbon species to the cast iron alloy that circulates in the casting direction, so that the final metallurgical quality can be adapted continuously to the requirements set by the production and according with the analytical control guidelines used in foundry.
• ATD Differential Thermal Analysis
• a cooling curve is the representation of the evolution of the temperature as a function of time, of a sample that has been cast in a standardized mold, with a thermocouple located in the center.
• T E i 0 w Lower eutectic temperature
• T Eh ⁇ gh upper eutectic Temperature
• the object of the invention is also a device for inoculating a nucleating additive to a cast iron alloy
• a device for inoculating a nucleating additive to a cast iron alloy comprising a transferred arc plasma torch and a casting distributor in which the plasma torch is disposed in said casting distributor located before the mold line, said plasma torch comprising an anode partially submerged in a cast iron alloy contained in the casting distributor and a cathode located on the surface of said cast iron alloy, to establish a plasma arc between the cathode and the surface of the molten alloy, comprising the anode or cathode or both graphite that provides said nucleating additive to the molten iron alloy.
• Graphite can be synthetic crystalline graphite.
• the anode may be provided with means to regulate the surface area of the anode that is submerged in the cast iron alloy. Being able to regulate the amount of anode that is immersed in the cast iron alloy allows to control the amount of anode that melts and therefore the amount of nucleating additive that is inoculated to the cast iron alloy from the anode.
• the control of the casting temperature is carried out by regular application of power depending on the temperature range set for each reference and the temperatures recorded in the distributor itself and / or in the pouring jet, that is to say , at the moment when the metal is transferred to the mold.
• inoculation on the other hand is regulated depending on the power applied at a given time.
• the immersion depth of the anode is reduced proportionally since the transfer of carbon species is preferably carried out from the cathode.
• the anode is submerged to a greater depth to offer greater dissolution surface and thus compensate for the lower transfer of carbon species by the cathode.
• the plasma torch may comprise means for regulating the power of the plasma arc.
• the laundry distributor may have a configuration selected from: 1) channel or a hotbed of a laundry oven. These ovens have a central storage tank and a loading mouth for filling the metal from the melting furnace. The vats are sealed and the metal moves to the pouring board due to the pressure of a gas that is injected into the tank. Nitrogen is commonly used to pressurize the tank because it is an inert gas that does not affect the composition of the metal, although in the manufacture of gray or malleable cast iron, air is used since they do not contain easily oxidizable elements. When the metal has reached its level of work on the board, the heating and inoculation of the bath by means of the electrodes begins.
• the metal is poured into the mold through the casting bucket mounted at the bottom of the piquera and located on the axis of the mold filling cup.
• the filling flow rate is regulated by the stopper or stopper cap.
• the metal level in the board is kept constant by regulating the pressure exerted inside the storage tank and is controlled on the surface by contact electrodes. In such a device, as shown in Figure 1, the anode can be found both upstream a-1 or downstream a-2 with respect to the cathode position (C) in the pier.
• This casting device is a simplification of the pressurized oven and basically consists of an open vat in which molten metal is poured and held during casting.
• the emptying system is It consists of the same elements, that is, a diver and stopper assembly and, unlike the previous one, the level of the metal in the trough is not constant as it descends as the laundry progresses.
• the effects of heating and inoculation are transmitted to the entire mass of stored metal and, as indicated in the diagram, the arrangement of the electrodes of the plasma system can be freely modified depending on the geometry of the trough. Also in this case, the anode can be found upstream a-1 or downstream a-2 with respect to the cathode position (C) in the pier.
• Tipping spoon This type of spoons is mainly used in horizontal molding lines and for medium-high mold weights (greater than 25 Kg) due to the difficulty of adjusting the flow rates by direct tilt to mold. Due to its special geometry, anode inoculation options are limited to the storage vessel by means of an anode that descends along with the metal level so that, in a maintenance situation. A location of the anode in position a-1 or a-2 can be chosen. However, the cathode can be placed in c-1 or c-2 depending on the particular needs of the smelter, c-1 being recommended for maintenance during waiting periods and c-2 for temperature control during casting.
• a spoon with transfer to laundry tray This is a variant of the tilting spoon in which the intermediate transfer from the nurse spoon to a pouring tray that is located on the axis of the mold filling cup is presented as an option.
• This system allows the assembly of a double plasma system in which a first plasma torch is available, with electrodes a-1 and c-1, installed in the feeding spoon or nurse, where the temperature is inoculated and maintained of metal
• the anode and cathode can be found in the casting distributor located on the circulation axis and emptying direction towards the cast iron alloy mold.
• the anode or cathode or both may be disposed within a closed chamber in an inert atmosphere.
• the plasma torch can act as a heating medium that can increase the temperature of the cast iron alloy for adjustment to a setpoint temperature, with a tolerance of less than ⁇ 5 5 C.
• Example 1 Inoculation stage during the manufacturing process of a gray cast iron part.
• the inoculation stage was performed statically in a tilting ladle (Fig 3).
• the metal used was gray cast iron (600 Kg added to the spoon).
• a crystalline synthetic graphite anode with a diameter of 50 was used mm
• the cathode used was 8 mm perforated synthetic graphite.
• the distance between anode and cathode was 230 mm.
• the immersion depth of the anode was 50 mm.
• Electrodes (anode and cathode) UHP (Ultra Hlgh Purity) whose characteristics are:
• Grain density 1.65 g / cm3.
• the test time was 95 min during which the bath temperature was kept constant at 1430 5 C.
• the average power applied was 57 Kw.
• the carbon content at the beginning of the test was 3.47% and the carbon content at the end of the test was 3.48% (both% by weight with respect to the total weight of the broth). Said content was determined by emission spectrometry and LECO.
• the temperature of the eutectic (Telow) at the beginning of the test was 1,147 5 C and the temperature of the eutectic at the end of the test was 1,151 C 5 .
• the anode consumption was 2.4 grams / Kw.
• the cathode consumption was 1.8 grams / Kw.
• Figure 5 shows the cooling curve of the cast iron alloy, indicating the evolution of TeLow and Recalescence.
• Example 2 Inoculation stage during the manufacturing process of a nodular cast iron part.
• the inoculation stage was performed dynamically in a casting channel with inductor (Presspour) (Fig 1).
• the metal used was nodular cast iron, with the weight of metal in the 280 kg channel and the pouring rate of 7.2 Ton / hour.
• the arrangement of the electrodes was with the anode upstream of the cathode.
• a synthetic crystalline graphite anode or with a diameter of 50 mm was used.
• the cathode used was 8 mm perforated crystalline synthetic graphite.
• Electrodes (anode and cathode) UHP (Ultra Hlgh Purity) whose characteristics are: Specific electrical resistivity: 6.5 ⁇ / meter
• Grain density 1.65 g / cm3.
• the distance between anode and cathode was 180 mm.
• the immersion depth of the anode was 70 mm.
• the test time was 180 min during which the bath temperature was maintained between 1390 and 1410 5 C.
• the average power applied by the plasma was 24 Kw and 150 Kw in the inductor.
• the temperature of the eutectic (Telow) at the beginning of the test was 1,138 5 C and the temperature of the eutectic at the end of the test was 1,141 C 5 .
• the anode consumption was 3.8 grams / Kw.
• the cathode consumption was 0.4 grams / Kw.
• Figure 6 shows the cooling curve of the cast iron alloy, indicating the evolution of TeLow and Recalescence.

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• 2009
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